Production and decomposition dynamics of hydrogen peroxide in freshwater

Hydrogen peroxide (H2O2) is widely recognised as the most stable of the reactive oxygen species produced by solar radiation-driven photochemical reactions in natural waters. H2O2 concentrations were determined in a shallow fresh water system (water of Leith, Dunedin, New Zealand) by flow-injection analysis (FIA) using an acridinium ester chemiluminescent reaction system. Daytime measurements of H2O2 concentration showed a rapid increase from early morning (15 nM) to 1300 hours (491 nM), consistent with photochemical formation, lagging maximum solar irradiance by similar to 1.5 h. The wavelength dependency of H2O2 formation was studied and it was shown that UV-B, UV-A and PAR contributed 40, 33 and 27%, respectively. The average formation rate was 339 nMh(-1) during springtime. The influence of biotic communities on the rate of H2O2 decomposition was also studied and the majority of decomposition was due to particles smaller than 0.22 mu m. The overall first order decay rate constant was of the order of 7.1 h(-1). The bacterial and algal communities in the water column and on the riverbed were primarily responsible for the decomposition of H2O2.